In optical networks, a distinction is drawn between wide area networks (Core networks), which are designed according to the SONET or SDH recommendations, and local loops or access networks. The access networks are designed as so-called Passive Optic Networks (PONs), in which the data transfer takes place in a first “wavelength channel” according to special PON protocols. In the “downstream direction”, the transfer takes place in the time-division broadcast mode from an exchange, mostly labeled with “Optical Line Terminal—OLT”, to a number of connected optical network terminals (ONU/ONT), which are individually addressed. “Upstream” the network terminals (ONU/ONT) split a second wavelength channel, in order likewise to send data to the exchange in the time-division operation in bursts or cells. The transmission capacity, called “bandwidth”, between exchange and network terminal can be varied. The reference data, called payload, are transmitted e.g. in the “Asynchronous Transfer Mode” (ATM) or, for reasons of cost, according to the Ethernet recommendations. The main advantage of an Ethernet PON lies in the avoidance of complex and therefore expensive ATM or SONET elements. The development of these networks is represented in the article “Gigabit Ethernet Passive Optical Networks” by Gerry Pesavento Senior and Mark Kelsey, Alloptic Inc. Livermore, Calif. 94550.
In the patent US 2003/0002776, a transmission system with a mesh-shaped metro core network run in the wavelength multiplex mode is described. Attached to the metro core network are bidirectional access connections which, in contrast to the conventional PON networks, work in the wavelength multiplex mode and therefore necessitate a corresponding complexity of connection.
A further development of the system described for higher data rates is laid down as GPON in the ITU recommendations G984. Developments newer than “Super PON” are outlined in IEEE Communications Magazine, February 2000, pages 74 to 82 under the title “The SuperPON Demonstrator: An Exploration of Possible Evolution Path for Optical Access Networks”. The goal of the development is both to expand the scope of these access networks and to enlarge the number of possible user connections. A simplification is thereby reached, in that so-called access nodes “Narrow Band Switches” are relocated from the access area to the Core network (FIG. 1, FIG. 2). However, the access area features active (amplified) splitter devices as before, which provide the optical network terminals (ONT/ONO) with sufficient optical capacity.
Moreover, the network described here also features the following disadvantages: in the access area optical regenerators—Optical Repeater Units (ORUs)—are required; the regenerators installed there are to be maintained as active elements. The range is too small for larger network structures in the metro area and in the purely passive area (indicated in FIG. 2 with “drop (10 km)”).